Modern mass rapid transit rail systems are very effective carriers of people. They are generally grade separated systems to enable vehicles to operate unaffected by automobile traffic, and thereby are able to achieve traffic densities otherwise unachievable. They are, however, very expensive. A typical, but conservative order of magnitude system capital cost for a system is approximately $100 million per bi-directional track mile of system, making it difficult for communities and cities to justify and/or afford the cost of new construction. This limitation has the effect of constraining the reach of these systems, and thus limiting the convenience to the users who can only ride the systems to the few locations to which guideway has been constructed. This results in a classic case of Catch 22. The high cost of systems requires a high ridership to justify the cost. However, high guideway costs limit construction and thus the reach of fixed guideway systems. This limits convenience to the riders, making it difficult to achieve the high ridership needed to justify the high cost.
Conventional mass rapid transit rail technology attempts to improve the ratio of benefits per cost by focusing on serving the commuting public. This means building systems to achieve very high passenger capacities to major employment centers. An example conventional system is shown in FIG. 1. As shown, conventional systems 110 achieve high capacities by building heavy infrastructure and operating long heavy trains 112 that typically carry a large number of riders to the few large employment centers 114, 116 that they can most effectively service, while bypassing smaller towns or communities 118, 120. This, however, requires very costly guideway 122 and station structures 124, 126, which limits the system's reach and thus convenience for the users, especially for those who want to travel to the generally more widely distributed retail, residential, or recreational destinations.
With guideway 122 and station structures 124, 126 that must be built to handle long heavy trains 112 to support demand during commute hours, the result is an expensive but marginally justifiable solution for commute hour travel which is far too expensive to justify for other periods of the day and other destinations.
Other existing transportation systems that aim to be less expensive to build and operate include automated people mover (APM) systems, such as those operating in many modern airports and some cities. These systems are low speed/low capacity systems that operate driverless vehicles at speeds in the range of 25 to 30 mph and achieve line capacities in the range of 2,000 to 3,000 passengers per hour per direction. Given the limited speed and capacity of these systems, even with the somewhat lower cost of construction due to the use of smaller vehicles, the benefit per cost is still poor. Furthermore, with the lower speeds and line capacities, these systems are limited in utility to local service routes.
Another type of transportation system that has been discussed is called “personal rapid transit” (PRT). PRT's differ from the more common APM systems in that these systems are built with offline stations which allow higher traffic densities to be achieved. Typically these systems operate driverless cars that seat four to six people and can provide service on a personal demand-driven basis. However, with the very small cars, high speeds are difficult to achieve and line capacities are severely restricted. Certain existing systems purport to be PRT systems, including a line at Heathrow Airport in London and one in the Masdar City district of Abu Dhabi, although with top speeds in the range of 25 mph, these systems cannot be truly considered “rapid transit.”
In both of the transportation modes described above, the low line capacities that can be achieved make the economic benefits to cost ratio poor. Because any fixed guideway technology requires expensive track infrastructure to be constructed even with smaller lighter cars, unless the service capacity can be made high, the cost of construction per passenger served is high, making it difficult to cost justify.
Co-pending application Ser. No. 13/218,422, the contents of which are incorporated by reference in their entirety, dramatically advanced the state of the art by providing a fixed guideway transportation system that can overcome many of the above and other challenges of the prior art. For example, the system of the co-pending application includes driverless vehicles carrying 10 to 30 persons that can achieve a line capacity that is equivalent to that which is achieved with the current day mass transit systems that achieve capacity with long and heavy trains. With a holistic understanding of the issues that drive the cost of transit, the invention of the co-pending application is designed to optimize the amount of benefits per cost of such systems. However, certain challenges remain.
For example, in order to cost effectively build and operate a system that operates smaller vehicles such as those contemplated by the co-pending application, yet achieves line capacities that justify the cost of constructing track infrastructures, the density of traffic that can be achieved should be sufficiently high. That means that the safe operating headways must be made smaller than that which is achievable with conventional control systems that represent today's state of the art. Furthermore, these safe operating headways should be achieved at mass rapid transit speeds (at least 60 mph). Quantifying the relationship between the achievable safe operating headway and the derived benefits and costs that result from the performance achieved, is a complex problem. It requires as inputs to the calculation, an understanding of how capital construction costs are affected by the weight of the vehicle, and how the cost of operating and maintaining a system is driven by vehicle weight and count. For simplicity, if the goal is that the ratio of benefits per cost must be improved by a factor of 4, this improvement could be achieved by operating 40 passenger vehicle consists (this could be 40 passenger vehicles, or smaller vehicles operated in a consist of multiple vehicles) with a safe operating headway of 9 seconds. However, this short headway cannot be achieved with current systems. Accordingly, there remains a need for a methodology for designing a system that provides the collision protection necessary to operate at a 9 second separation at these high traffic densities.
Relatedly, since a collision between two vehicles is a life-threatening event, control functions that prevent collisions are critical to safety. In the rail industry, control that is critical to safety must be designed and implemented to a standard commonly referred to as “vital.” In recent years achieving vital status has required an analytical demonstration of a Mean Time Between Unsafe Event or Hazard (MTBH) of 109 hours or greater. Accordingly, any methodology aimed at increasing traffic density should include collision protection satisfying this standard.